1. Field of the Invention
The present invention relates to a wireless integrated circuit (IC) device, and more particularly, to a wireless IC device including a wireless IC that is used in radio frequency identification (RFID) systems.
2. Description of the Related Art
For example, an RFID tag described in Japanese Unexamined Patent Application Publication No. 2007-102348 is a known wireless IC device used in access management, commuter passes, credit cards and other suitable applications. FIG. 14 is an exploded perspective view of an RFID tag 500 described in Japanese Unexamined Patent Application Publication No. 2007-102348.
The RFID tag 500 illustrated in FIG. 14 includes antenna substrates 502a to 502d, chip connection terminals 506a and 506b, an IC chip 508, sealing resin 510, and an antenna coil L. The antenna coil L is defined by antenna patterns 504a to 504d and through holes b501 to b504.
The antenna substrates 502 are rectangular-shaped insulator layers. The antenna patterns 504a to 504d are line-shaped conductors that each have a spiral shape and are respectively provided on the antenna substrates 502a to 502d. The through hole b501 connects the antenna patterns 504a and 504b to each other. The through hole b502 connects the antenna patterns 504b and 504c to each other. The through hole b503 connects the antenna patterns 504c and 504d to each other. The through hole b504 connects the antenna patterns 504a and 504d to each other.
The chip connection terminal 506a is provided on the antenna substrate 502a and is connected to the antenna pattern 504a. The chip connection terminal 506b is provided on the antenna substrate 502a and is electrically connected to the through hole b504. The IC chip 508 is mounted on the chip connection terminals 506a and 506b. Then, the IC chip 508 is protected by being covered with the sealing resin 510.
In the RFID tag 500, the antenna coil L and the IC chip 508 are connected to each other. Thus, the RFID tag 500 exchanges signals with a reader/writer, which is not illustrated.
In the RFID tag 500 described in Japanese Unexamined Patent Application Publication No. 2007-102348, the through hole b501 and the through holes b502 to b504 extend parallel to one another. Therefore, floating capacitances are respectively generated between the through hole b504 and the through holes b501 to b503. The generation of such floating capacitances causes the resonant frequency of the RFID tag 500 to deviate from a desired value.